Dragon Age II: Legacy is a DLC (downloadable content) for Dragon Age II. Hawke keeps getting attacked by Carta goons and now he brings the fight to them. However, it seems they are manipulated by some mysterious force and want to drink Hawke's blood. During the course of the game, Hawke will learn more about his family history.
Regarding gameplay, there are no significant changes to the main game. The content is arranged as a linear dungeon crawl intersected with dialogues, background information found in documents and some mini bosses; there are also three side quests on the way. Toward the end there is one puzzle to solve and one morale choice to take. The boss heavily relies on micro-managing the party and the reward is some powerful equipment. The content can be started at any time after reaching Kirkwall during the main story line, but a return is only possible at certain points.